It is known to apply a coating compound onto fresh poured concrete to minimize evaporation of moisture from the surface, and thereby to avoid or to minimize the occurrence of shrinkage cracking in the concrete. Such coating compounds typically comprise the use of a resin or wax dispersed in a water-based or petroleum oil-based carrier. The coatings are typically sprayed onto fresh concrete, and left in place for several days or weeks, such that a coherent membrane is formed after evaporation of the water or solvent from the sprayed coating. If paint or a bituminous layer is applied afterwards, the coating must be completely removed to avoid defeating the adhesion of ensuing coating materials. The coating can be removed by sandblasting or by scarification. The removal step can therefore be expensive and time-consuming. For example, sandblasting is labor-intensive because it is important to remove all resins or wax residues to expose the concrete surface or otherwise subsequent coatings or paints will not properly adhere to the concrete.
In addition to coating concrete surfaces to retard its setting, it is also known to apply coating materials to the inner surfaces of a form for molding the concrete. For example, U.S. Pat. No. 5,236,975 of Sekine disclosed the use of a coating material for preventing the setting of the surfaces of cement mortar that maintain contact with the coating material. The coating material taught by Sekine is a powdered polymer, having a high water absorption characteristic, which is made from mixing propylene glycol with maleic anhydride and either phthalic anhydride or isophthalic acid. The coating material can be removed by water washing, and decorative materials or patterns can be applied subsequently to the exposed surface of the concrete.
U.S. Pat. No. 5,389,172 of Kobayashi et al. disclosed a finishing method for exposing aggregate in concrete which is purportedly capable of reducing the usage of decorate aggregate and avoiding long working times. The method included the steps of loading aggregates onto an adhesive sheet, burying part of the aggregates in an adhesive layer of the adhesive sheet; casting mortar or concrete onto an aggregate loading surface of the aggregate loading adhesive sheet, hardening the mortar or concrete, and removing the adhesive sheet.
U.S. Pat. No. 4,205,040 of Aoyama et al. disclosed an exposed aggregate finishing method for concrete which comprises the following steps according to the abstract of the invention: coating the inside faces of a form for concrete with a cement setting retarder, drying, coating the dried faces with a synthetic organic polymer coating material which is soluble in an aqueous alkaline solution of cement but is insoluble in water, and drying the coated faces. Alternatively, the method could be carried out by coating the inside faces of the form for concrete with a mixture of the cement setting retarder and the organic polymer coating material and drying the coated faces. Concrete is thereafter placed in the concrete form, the form removed, and the surface of the molded concrete washed to make the surface rough.
As noted in Aoyama, the coating composition can include a surface retarder for treating the surface of concrete compositions. Fresh concrete containing aggregates is poured and leveled, and then the surface retarder is sprayed onto the surface at a rate of approximately 200 g/m2. After a number of hours, the treated surface is washed off with a jet of water under high pressure to remove uncured cement and to expose the aggregates on the surface.
Conventional surface retarders are typically water-based or solvent-based. The retarding agent “actives” (e.g., sucrose, organic acids or their salts, etc.) are either dissolved in water or suspended in a solvent. Solvent-based retarders are derived from petroleum distillates, and are typically less sensitive to the effects of rain and sun, but are not favored from an environmentalist's viewpoint. Water-based surface retarders, while environmentally friendly, suffer in terms of performance when exposed to high heat or sunlight, because they are susceptible to evaporation.
More recently, U.S. Pat. No. 7,037,367 of Mauchamp et al. disclosed the use of vegetable or mineral oil-based surface retarders. One advantage of using such vegetable or mineral oil-based set retarders was that they could provide a wet film coating, which, in turn, provided the retarder actives a favorable opportunity to penetrate into the surface of the mortar or concrete. Maintaining this penetrating ability facilitated the ability of the surface retarder to etch the treated surface of the mortar or concrete.
It is an objective of the present invention to provide a novel method, for applying coating materials to mortars and concretes, which avoids the use of resins or waxes dissolved in solvent, thereby avoiding VOC emissions and the need for sandblasting to remove the coating.
It is also an objective of the present invention to provide a method for applying coating compounds which avoids the use of resins or waxes in water, thereby achieving high performance in terms of minimizing or avoiding evaporation of moisture from the mortar or concrete. The methods of the invention also achieve superior performance, in terms of minimizing moisture evaporation from the mortar or concrete, without resorting to the use of plastic sheets, which can create waste disposal problems.